The UK must prepare for a "hard winter" because the population immunity to respiratory viruses other than Covid could be lower than usual, one of England's top medics has warned.

Dr Susan Hopkins said the NHS must be "ready" for surges in flu and other similar illnesses.

It comes ahead of England's first step towards easing lockdown, with all pupils returning to school on Monday.

Most pupils have been learning from home since Christmas.

Dr Hopkins, who is in charge of Public Health England's Covid strategy, said the UK needed to be "better prepared" than it was last autumn, when new, faster-spreading variants of the virus emerged.

These drove infection rates up and forced further lockdown measures over the winter.

Dr Hopkins told the BBC's The Andrew Marr Show: "I think we have to prepare for a hard winter, not only with coronavirus, but we've had a year of almost no respiratory viruses of any other type. And that means, potentially the population immunity to that is less.

"So we could see surges in flu. We could see surges in other respiratory viruses and other respiratory pathogens."

Dr Hopkins said her role as a government advisor was to "prepare for worst-case scenarios".

"It doesn't mean that they'll necessarily happen, but my job is to make sure that we have options available for the country in case things are not as satisfactory as we'd all like them to be," she said.

During last year's winter, some 30 million people - more than ever before - were invited to get a free flu jab as ministers feared the dual threat it posed alongside coronavirus.

Flu can be a serious condition - it kills around 11,000 people in England each year and many more people receive hospital treatment for it.